1. Field of the Invention
The present invention relates generally to communication systems. More particularly, the present invention relates to preserving a communication link.
2. Background
The widespread use of the Internet as a daily research, entertainment, and communication tool has increased the deployment of modems and other communication devices. There are instances during a communication session where a user may wish to place the communication on hold or cease the data communications, but yet preserve the communication session in order to proceed with data communications after the hold is removed. As discussed in the above-incorporated patent applications, one such instance may arise when a communication session is interrupted by a call waiting alert signal. As a result, the communication device receiving the call waiting alert signal may request that the remote communication device be placed on hold while answering the call waiting.
While such request advises the remote communication device of the hold situation, a higher-level data protocol would remain unaware of the data communication hold situation. Therefore, such higher-level data protocol would continue to transfer data and would eventually time out due to receiving no response from its remote counterpart.
For example, one such higher-level protocol that has gained popularity in the recent years is called Point-to-Point Protocol or PPP. PPP is a data link protocol that provides dial-up access over serial lines. PPP can run on any full-duplex link from POTS (Plain Old Telephone Service) to ISDN (Integrated Services Digital Network) to high-speed lines (T1, T3, etc.). PPP has become popular for Internet access as well as a method for carrying higher level protocols. PPP is a version of the Internet software that may run over telephone lines using high-speed modems. Furthermore, PPP allows a connection to the Internet without using an Internet service provider or an access point to the Internet. PPP may also be used for connecting a home computer to a larger local network, which is connected to the Internet.
In short, PPP provides a method for transmitting data over serial point-to-point links. PPP contains three main components: a method of using High-Level Data Link Control (“HDLC”) for encapsulating and transmitting data over serial links, an extensible Link Control Protocol (“LCP”) for establishing, configuring and testing the serial links and a family of Network Control Protocols (“NCP”) for establishing and configuring different network-layer protocols.
One class of LCP packets used for link management and maintenance includes echo-request to aid PPP for serial link quality determination, performance testing and for numerous other functions. In response to an LCP echo-request, a PPP layer must respond by transmitting an LCP echo-reply, otherwise the remote PPP layer may terminate the communication session. It should therefore be clear that in situations where the communication session is placed on hold, such as modem on hold, the PPP layer may terminate the communication session as a result of failing to receive an LCP echo-reply.
Accordingly, there is an intense need in the art for a communication device that is capable of preserving the communication session while the communication session has been placed on hold or is temporarily unable to proceed with data communications.